1. Field of the Invention
The present invention relates to an evaporated fuel treatment apparatus which temporarily adsorbs fuel components within an evaporated fuel to conveniently discharge the evaporated fuel to an intake passage in order to prevent the emission to the atmosphere of the evaporated fuel generated in a fuel tank of an internal combustion engine.
2. Description of the Prior Art
Conventionally, the evaporated fuel treatment apparatus of the type mentioned above is generally called a canister, and is known, for example, from Laid-open Japanese Patent Application No. Hei 7-332171. This canister comprises a box-shaped casing; three chambers, a first through a third chamber defined by partitioning the casing by partition walls; and active carbons filled in each chamber. The first and second chambers, and the second and third chambers communicate with each other. The first chamber is connected to an intake pipe through a purge passage, and is also connected to a fuel tank through a charge passage and a fuel supply charge passage. The fuel supply charge passage is larger than the charge passage for passing a large amount of evaporated fuel generated in a fuel tank during refilling, and a charge electromagnetic valve is provided midway in the fuel supply charge passage for opening and closing the same.
The second chamber is connected to a fuel supply discharge passage in communication with the atmosphere. A discharge control electromagnetic valve is provided midway in the fuel supply discharge passage. Further, the third chamber is connected to an atmosphere passage in communication with the atmosphere. The fuel tank is also provided with a switch which is turned ON when a fuel supply port lid is opened.
In the canister, during a normal operation other than refilling, an evaporated fuel generated in the fuel tank is first introduced into the first chamber through the charge passage, and then introduced into the second chamber and third chamber in this order. In this event, as the evaporated fuel passes through each chamber, fuel components such as hydrocarbons (HC) are adsorbed on the active carbons, and then emitted to the atmosphere through the atmosphere passage. On the other hand, when the fuel is supplied, the fuel supply port lid of the fuel tank is opened, causing the switch to turn ON, the charge electromagnetic valve and discharge control electromagnetic valve are opened in response to the switch. In this manner, the evaporated fuel generated in the fuel tank due to the refilling is introduced into the first chamber through the fuel supply charge passage, next introduced into the second chamber, and then emitted to the atmosphere through the fuel supply discharge passage. Also, when a negative pressure in an intake pipe is introduced into the first chamber through the purge passage due to the operation of the engine, air in the atmosphere flows into the third chamber, second chamber and first chamber in this order through the atmosphere passage. In this event, the fuel components adsorbed on the active carbons are desorbed and sent to the intake pipe together with the air through the purge passage.
As described above, in the canister, the evaporated fuel is introduced into the three chambers in the normal operation, and introduced only into the first chamber and second chamber during refilling. The reason for this operation may be described as follows. In the normal operation, the longest possible length of the flow passage is ensured for the evaporated fuel when it flows through the active carbons in the canister to improve the adsorption performance provided by the active carbons for the evaporated fuel. On the other hand, during refilling, where a larger amount of evaporated fuel is generated than during the normal operation, the length of the flow passage is reduced, as compared with that in the normal operation, to reduce the air-flow resistance in the canister to suppress a rise in the pressure within the fuel tank during refilling caused by the evaporated fuel and thereby reduce a time required for supplying the fuel to the fuel tank.
The conventional evaporated fuel treatment apparatus requires the discharge control electromagnetic valve, fuel supply discharge passage, switch and the like provided for reducing the refilling time, thereby resulting in a correspondingly complicated structure and an increase in the manufacturing cost. Also, the discharge control valve is susceptible to a leak of evaporated fuel. Further, since the first, second and third chambers are defined by partitioning the casing with the partition walls to limit the areas of the active carbons within the casing which are in contact with the external air through the wall of the casing, the active carbons are prevented from changing the temperature through heat exchanging with the external air. This may fail to provide satisfactory adsorption/desorption performance for the evaporated fuel by the active carbons.
The present invention has been made to solve the foregoing problems, and it is an object of the invention to provide an evaporated fuel treatment apparatus which is capable of reducing a refilling time, ensuring satisfactory adsorption/desorption performance for an evaporated fuel, and reducing the manufacturing cost through simplification of the structure.
To achieve the above object, the present invention provides an evaporated fuel treatment apparatus for introducing an evaporated fuel generated in a fuel tank of an internal combustion engine to discharge the evaporated fuel to an intake passage, and emitting the evaporated fuel to the atmosphere after adsorbing fuel components contained in the evaporated fuel. The apparatus includes a casing having formed therein a main chamber in communication with the fuel tank, and a sub-chamber in communication with the main chamber and the atmosphere, respectively, a main adsorbent contained in the main chamber to adsorb fuel component in an evaporated fuel introduced from the fuel tank, and a sub-adsorbent contained in the sub-chamber to adsorb fuel components in the evaporated fuel introduced from the main chamber before the evaporated fuel is emitted from the sub-chamber to the atmosphere, wherein the sub-chamber including the sub-adsorbent has an air-flow resistance which is set smaller than an air-flow resistance of the main chamber including the main adsorbent.
According to the evaporated fuel treatment apparatus, an evaporated fuel generated in the fuel tank is introduced into the main chamber, and then introduced into the sub-chamber before it is emitted to the atmosphere. In this event, the evaporated fuel is emitted to the atmosphere after fuel components contained therein are adsorbed by the main adsorbent and sub-adsorbent. In this manner, the evaporated fuel generated in the fuel tank flows along the same flow passage either during refilling or during a normal operation, unlike before, so that the same length can be ensured for the flow passage during refilling as that during the normal operation. Since the air-flow resistance of the sub-chamber including the sub-adsorbent is set smaller than that of the main chamber including the main adsorbent, it is possible to suppress a rise in the overall air-flow resistance of the main chamber and sub-chamber during refilling. Also, the main fuel adsorbent in the main chamber, having a larger air-flow resistance adsorbs, a majority of fuel components in the evaporated fuel, while the sub-adsorbent in the sub-chamber complementally adsorbs the remaining fuel components, thereby making it possible to effectively adsorb the fuel components in the evaporated fuel, and maintain satisfactory adsorption performance. This can lead to a reduction in refilling time during refilling, and to the satisfactory adsorption performance ensured for the evaporated fuel. In addition, since the present invention eliminates an electromagnetic valve, a discharge passage and the like for refilling, which have been conventionally required, the structure can be correspondingly simplified to reduce the manufacturing cost.
Preferably, in the evaporated fuel treatment apparatus, the sub-adsorbent has a slitted cross-section.
According to this preferred embodiment of the evaporated fuel treatment apparatus, the sub-adsorbent can be relatively easily manufactured.
Preferably, in the evaporated fuel treatment apparatus, sub-adsorbent is formed in a honeycomb shape.
According to this preferred embodiment of the evaporated fuel treatment apparatus, the sub-adsorbent surpassing in the strength can be relatively easily manufactured in an integral form.
Preferably, in the evaporated fuel treatment apparatus, a portion forming the main chamber of the casing and a portion forming the sub-chamber are arranged such that they are spaced apart from each other.
According to this preferred embodiment of the evaporated fuel treatment apparatus, the two portions of the casing are arranged such that they are spaced apart from each other, so that larger contact areas can be ensured for the two portions of the casing in contact with external air, thereby making it possible to effectively cool or heat the adsorbents within the casing through heat exchanging with the external air. As a result, the adsorption/desorption performance can be improved for the evaporated fuel.